Light metal cylinder block, method of producing same and device for carrying out the method

ABSTRACT

Thc present invention includes a light metal cylinder block comprising a cylinder running face which is coated with silicon. The invention also includes a method by which the silicon is applied to the running face comprising melting powder metal silicon, which is fired at the face in a powdered metal beam, under heat of a laser which is fired at the running face at the point of impact of the powdered beam. Furthermore the invention includes a device with which the cylinder block may be manufactured.

FIELD OF THE INVENTION

[0001] The invention relates to a light metal cylinder block having atleast one wear-resistant and tribologically optimised cylinder runningface, comprising a light metal matrix alloy and a powder material whichcontains a hardening material and which is present on the light metalmatrix in the form of a finely dispersed surface layer containingprimary silicon precipitations. The invention also relates to a methodby which to produce the blocks and a device with which to produce theblocks.

BACKGROUND OF THE INVENTION

[0002] According to EP 0 837 152 A1(Bayerische Motoren Werke AG), thereis known a method of coating a component of an internal combustionengine, which component consists of an aluminium alloy. A laser beam isdirected in such a. way that it does not directly reach the surface ofthe component to be coated, but first hits a powder beam. As a result ofthe energy of the powder beam, the powder is transformed completely fromthe solid phase into the liquid phase, so that the powder, when hittingthe component surface, is separated in the form of fine droplets as acoating material on the component surface, which fine droplets, as aresult of the solidification conditions. solidify so as to be partiallyamorphous

[0003] Therefore, in the case of the prior art method, the powder is notalloyed into the surface layer of the component, but there takes place aphase transformation of the coating material on its way to the surfacewith the aluminium silicon powder being liquefied in the laser beam.When the powder solidifies on the surface the object is to release afinely dispersed silicon, a so-called primary silicon.

[0004] Depending on the cooling speed, the purpose is to produce siliconcrystals whose size ranges between 1 to 5 μm. However. rapid cooling, asrequired. cannot be achieved in practice because of the energy of thelaser beam acting on the component to be coated. In consequence, thesubstrate surface heats up very quickly and therefore cannot dischargethe heat of the arriving Si melt quickly enough. so that instead of acrystalline phase and primary crystals, there occurs an amorphous phase.

[0005] In accordance with the embodiment of the BMW patent, in the caseof an applied layer thickness of 3 mm, approximately 50% are removed toachieve a smooth, planar surface of the coating material (column 6,lines 10 to 15). This means high removal losses and an unused boundaryzone as a result of the pronounced waviness of the material applieddrop-wise, which constitutes an additional disadvantage.

[0006] Furthermore, it is known from EP-A-0, 221, 276 to render analuminium alloy more wear-resistant by remelting its surface layer bylaser energy. A layer consisting of a bonding agent, silicon in powderform, copper and titanium carbide is applied to the surface andsubsequently melted into the surface by laser. According to theembodiments listed. TIC is added in amounts ranging between 5% and 30%and achieves a considerable increase in the surface hardness. However,from a tribological point of view the extremely high cooling speedduring laser remelting achieves a high degree of core fineness, but asufficient amount of primary silicon cannot be produced with thismethod. Therefore, laser remelting is not suitable for producingcylinder running faces of reciprocating piston engines consisting ofAlSi alloys with supporting plateaus of primary silicon and set-backregions containing lubricants.

[0007] EP 0 411 322 describes a method for producing wear-resistantsurfaces of components made of an AlSi alloy, which method is based onthe previously mentioned EP 0 211 276, but prior to carrying out thelaser remelting process, the layer is provided with an inoculation agent(germ forming agent) for primary silicon crystals. The followingsubstances are mentioned as inoculation agents or germ forming agents:silicon carbide titanium carbide, titannitride, boron carbide andtitanium boride.

[0008] In a preferred embodiment, the coating is produced by silk-screentechnology in the form of a peel-off coating and applied to the surfaceof the component concerned. The coating thickness can preferably amountto 200 μm and the melting-in depth can amount to 400 to 600 μm. Use ismade of a linearly focussed laser beam in an inert atmosphere to be ableto achieve a melting-in depth of 400 μm. In the example given, thesilicon content in the alloyed zone amounted to 25% with a nickelcontent of 8% (hardness in excess of 250 HV).

[0009] As already mentioned above, it is necessary, in the case of thelatter processes of remelting and melting-in, to carry out a coolingprocess while applying a coating on to the matrix alloy in order toachieve the required finely dispersed segregations of primary silicon.Because of the addition of inoculation agents reactions can take placeon the aluminium surface In addition the coating measures cannot alwaysbe applied to curved surfaces.

[0010] EP 0 622 476 Al proposes a metal substrate with a laser-inducedMMC coating. The MMC coating comprises a coating thickness between 200μm and 3 mm and contains homogeneously distributed SIC particles; in apreferred embodiment, up to 40% by weight of SiC is contained in the MMCcoating in the form of homogeneously distributed SIC particles. Forproduction purposes, the powder mixture containing SiC powder andpre-alloyed AlSi powder is heated in a laser beam, with the heat contentrequired for producing a homogeneous alloy from the powder mixture beingprovided by the powder applied to the substrate. Products containinghard metal materials such as SiC comprise a very high hardness which isdisadvantageous for the wear behaviour of the piston rings. Furthermore,machining is very complicated and expensive because the top layer of theceramic particles has to be removed in order to achieve a functionable,splinter-free running face.

SUMMARY OF THE INVENTION

[0011] The invention includes a light metal cylinder block having atleast one wear-resistant and tribologically optimized cylinder runningface, comprising a light metal matrix alloy with a finely dispersedsurface layer containing primary silicon phases, wherein the primarysilicon comprises uniformly distributed approximately roundly formedgrains with a medium grain diameter ranging between 1 and 10 μm andwherein the surface layer contains about 10 to about 14% AlSi eutectic,about 5 to about 20% primary silicon. the remainder being pure Al phase,and wherein the minimum hardness on the Surface amounts to about 160 HV.

[0012] Furthermore, the invention includes a method of producing a lightmetal cylinder block having at least one wear-resistant andtribologically optimized cylinder running face, comprising a light metalmatrix alloy and a powder material which contains a hard material andwhich is present in the form of a finely dispersed surface layer withprimary silicon precipitations in the light metal matrix, using agravity, low-pressure or high-pressure die casting method withsubsequent surface treatment by parallel laser and powder beams whereinthe laser beam is guided in a strip width of at least 2 mm transverselyto the direction of feed across the matrix surface and wherein it isonly in the point of impact of the laser beam on the light metal matrixsurface in a contact time of 0.1 to 0.5 seconds, that the powder isheated to melting temperature and diffused in.

[0013] The invention also includes a device for coating the a runningsurface of a hollow cylinder, comprising powder supply means (1), alaser beam device (2) and a focusing system (3) with a deflecting mirror(4), characterized in that the powder supply means (1) and the laserbeam device (2) are guided parallel relative to one another in theradial and axial direction of the hollow cylinder; that the focusingsystem (3) comprises a linear beam exit with a beam width of 2.0 to 2.5mm; and that the powder supply means are provided with a metering deviceby means of which the volume flow of the powder can be set as a functionof the speed of feed of the laser beam.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014]FIG. 1, in the form of a partial cross-section illustrates theprinciple of a coating device designed in accordance with the invention.

[0015]FIG. 2 illustrates the principle of a surface layer produced inaccordance with the invention.

[0016]FIG. 3 shows a comparative example having a different surfacestructure.

[0017]FIG. 4 is across-section of a casting in the region of thelaser-alloyed zone.

DETAILED DESCRIPTION OF THE INVENTION

[0018] It is an object of the present invention to develop a light metalcylinder block having at least one wear-resistant and tribologicallyloadable running face, wherein the surface layer comprises about 5 toabout 20% of finely dispersed primary silicon which, in the region oftransition to the matrix alloy, comprises a narrow boundary zone widthand which is free from defects and oxide inclusions in the transitionzone. Preferably the block comprises a finely dispersed surface layercontaining primary silicon phases, wherein the primary silicon comprisesuniformly distributed approximately roundly formed grains with a mediumgrain diameter ranging between about 1 and about 10 μm and wherein thesurface layer contains about 10 to about 14% AlSi eutectic (e.g., 10,11, 12, 13 or 14%), about 5 to about 20% primary silicon (e g., 5, 6, 7,8, 9, 10, 1, 12, 13, 14, 15, 16, 17, 18, 19 or 20%), the remainder-being pure Al phase, and wherein the minimum hardness of the surfaceamounts to at least about 110 HV. preferably at least about 160 HV.Furthermore, the silicon primary phases in the coated block may bedistributed in the surface layer at a distance of 1-5 times (e.g., 1, 2,3, 4 or 5 times )the primary phase diameter. The primary silicon may bearranged in a strip-like manner wherein the strip width is about 2 mm ormore (e.g., 2, 3, 4, 5, 6, 7, 8, 9, 10, 11 or 12 mm or more),preferably, about 2 mm to about 4 mm. The thickness of the strip may beabout 150 μm to about 650 μm. The strips may also overlap wherein thewidth of overlap is from about 5% to about 10% (e.g., 5, 6, 7, 8, 9 or10%) of the total strip width.

[0019] A method used for producing the light metal cylinder blocksshould have fewer process stages, and a subsequent chemical treatment isto be eliminated completely.

[0020] The objective is achieved by the characteristics given in theclaims. Below, several embodiments will be referred to; they representpreferred applications of the laser alloying method in accordance withthe invention.

[0021] First, a device for coating the interior of a light metal engineblock made of aluminium or a magnesium alloy, wherein a probe in loweredinto the cylinder of the engine block with pure silicon powder beingintroduced at the same time will be described. The probe comprisespowder supply means and a laser beam device.

[0022] A rotary drive arranged at the probe directs a powder ejectionnozzle and an energy beam on to the interior (i.e., the running face ofthe light metal cylinder block).

[0023] The purpose of this device is to alloy hard material particles inthe form of silicon by means of a laser beam rotating spiral-like acrossthe running face into silicon particles supplied in parallel. To ensurethat the laser energy is distributed over a wide track on to the matrixsurface, the laser beam comprises a linear focus with a trick widthabout 2 mm or more (e g , 2, 2, 5, 3, 4, 5, 6, 7, 8, 9, 10, 11 or 12 mmor more). preferably about 2 to about 4 mm. As compared to a surfaceproduced by a spot beam, a focus does not result in a wavy profile, butin a flat band with finely dispersed primary silicon particles. The bandis referred to as alloyed-on zone and there is only a narrow transitionzone (of the boundary zone) between the alloyed-on zone and the matrixmetal (see FIG. 1). The alloyed-on zone may penetrate the face at anydepth; for example, 100, 200, 300, 350, 400, 500, 600, 700, 750, 800,850, 900, or 1000 μm.

[0024] The powder comprises a grain structure shortly before hitting themetal matrix alloy and is melted and alloyed-in only when coming intocontact with the metal matrix alloy in the region of the laser beamwithin a contact time of about 0.1 to about 0.5 seconds (e.g., 0.1, 0.2,0.3, 0.4 or 0.5 seconds), so it is possible, by means of the linearfocus, to achieve a small boundary zone percentage of approx. 10%. Thepowdered metal beam may be fed at a rate of about 0.8 to about 4.0meters per minute (e.g., 0.8, 1, 1.2, 1.5, 2, 2.5, 3, 3.5, or 4 metersper minute). The laser may be focused to have an impact area of about 1mm² to about 10 mm²(e.g., 1, 2, 3, 4, 5, 6, 7, 8, 9 or 10 mm²) with alaser light output of about 3 kW to about 4kW (e.g., 3, 3.25, 3.5, 3.75or 4 kW). The light metal matrix alloy, at the point of beam impact, maybe fully melted ,at a depth of about 350 μm or more (e.g.,350, 375,400,450, 500, 600, 700, 800, 850 or 900 μm), and transferred to a plasmacondition. The melted powder may form an alloyed-on zone which comprisesa layer thickness of about 500 μm to about 1000 μm (e.g., 500, 600, 700,800, 900 or 1000 μm). The laser track is lowered spiral-like in thecylinder- bore, and overlapping can be eliminated, if necessary, so thatthe effective parts practically about one another. There is thusproduced a smooth, completely homogeneous surface layer which only needsto be finished by precision machining to eliminate a slight waviness.

[0025] As an example of the inventive machining operation applied whenproducing light metal cylinder blocks with at least one wear-resistant,tribologically optimised cylinder running face the following machiningstages take place:

[0026] First, an alloyed-on zone containing primary silicon with a meanlayer thickness of about 300 to about 750 μm (e g, 300, 350, 400, 450,500, 550, 600, 650, 700 or 750 μm) is produced in the matrix alloy. Theexact values of the layer thickness depend on different influencingfactors such as process parameters, positioning accuracy of the deviceand dimensional tolerances of the casting. Therefore, when thicknessesare given below, reference is always made to a “mean” layer thickness,and the tolerance range can be kept very narrow because the device canbe centred at the component. The alloyed-on zone may be applied instrips wherein the strip width is about 2 mm or more (e.g., 2, 3, 4, 5,6, 7, 8, 9, 10, 11 or 12 mm or more), preferably, about 2 mm to about 4mm.

[0027] In a further machining stage, the starting layer thickness ofabout 300 to about 750 μm is then reduced by precision machining, suchas honing, to the required end layer thickness by removing up to about150 μm. The alloyed-on zone may be honed directly without anintermediate machining operation. Preferably, the uppermost layer ofalloyed-on zone which is removed does not exceed about 30% of totallayer thickness (e.g., 5, 10, 15, 20, 25 or 30%). The end layerthickness achieved by the inventive method ranges between about 150 andabout 650 μm (e.g., 150, 200, 250, 300, 350, 400, 450, 500, 550, 600 or650 μm). 1 and 2.

[0028] The segregation values of the hard phases can be set bycontrolling the powder supply the laser beam feed and the laser energysupplied. In the case of precipitation values smaller than about 10 μm,the destruction depth while finish-machining the hard phases is reduced,so that the previously required machining allowances for removing thedestroyed hard phases can be reduced considerably. (The destructiondepth is determined by the hard phases which are contained in the toplayer and which are not firmly bonded in )

[0029] By using the laser beam for alloying-in purposes, the surface ishardened, with surface layer hardness values of at least about 110 HV,preferably about 160 HV or more (e g., 110, 130, 145, 160, 200, 300, 400or 500 HV) being achieved. Because of the good hardening results, thelaser-treated surfaces can be honed directly. Furthermore, previouslyrequired additional mechanical and chemical treatment stages forexposing the hard phases are no longer necessary. This also means thatit is no longer necessary to bore out the cylinder coatings because,depending on the degree of overlap of the strip-like alloyed-on zone,the surface waviness is negligibly small.

[0030] Below, the surface structure achievable in accordance with theinvention on an engine block running face will be described in greaterdetail with reference to a comparative example.

[0031] As illustrated in Figure 1, the coating device designed inaccordance with the invention comprises powder supply means 1 which, attheir end 1 a, comprise a nozzle 1 b directed towards the running face 5

[0032] The energy is supplied by, a laser beam device 2, a focussingsystem 3 and a deflecting mirror 4 which ensure that the laser beam doesnot meet the powder close before it hits the running face surface 7

[0033] According to the known laws of optics, the laser beam 6 isfocussed so as to be linear, preferably X-, I- or 8-shaped and thencopied on the running face surface 7, for example by tilting the mirror.The amount of energy introduced can be controlled by the form of thecopy, so that the precipitation structure can be influenced at theboundaries.

[0034] By turning the mirror 4, the laser beam 6 moves across therunning face surface 7, so that a strip-like band is obtained. If, atthe same time, the laser beam 6 is moved forward towards the cylinderaxis 8, the overlapping of the two movements results in a spiral-likecoating on the running face surface 7. The rotating movement and thetranslatory movement towards the cylinder axis 8 should be adjusted toone another in such a way, that the windings of the spiral are closetogether, thus achieving a closed alloyed-on zone.

[0035]FIG. 2 shows the alloyed-on zone 10 produced with a linear focusin accordance with the invention and including a zone 11 high inprecipitations and laterally arranged zones 12, 13 low inprecipitations. FIG. 2 shows the condition of the alloyed-on zonedirectly after laser treatment, and it can be seen that the percentageof the zone L_(AL) low in precipitations is relatively low, relative tothe effective length L_(NL) of the zone which is high in precipitations.The respective regions in figure 3 have been given the reference symbolL_(AK) and are associated with the interface zones 15, 16, 17

[0036] For comparative purposes. FIG. 3 shows three alloyed-on /onesproduced with a conventional circular focus. The coating width producedby a linear locus is approximately identical to that produced by acircular focus. It can be seen that in the case of the method using acircular focus the effective length L_(NK) of the structure high inprecipitations is considerably shorter than the effective length L_(NL)achieved by a linear focus. Furthermore, in the case of a circularfocus, the effective depth of the hardened surface layer is very muchshorter than in the case of the linear focus, because in the case of thecircular focus, a structure low in precipitations extends down to thedeeper zones of the cylinder block structure. This is illustrated in thecross-section according to FIG. 3 by the wide interface zones 15, 16,17.

[0037] As with the same depth of penetration, the effective depth in thecomparative example according to FIG. 3 is shorter than in the inventiveexample according to FIG. 2, the coating quality in the comparativeexample is lower. Furthermore, with the machining depth being the samein the comparative example and in the example according to theinvention, the amount of material ΔH_(WK) having to be removed in thecomparative example is considerably higher (ΔH_(WL)) because thecircular focus produces a wavy surface layer which, in the region of therunning face, comprises a smaller effective material percentage M_(K)than a corresponding running face portion according to FIG. 2 (L_(NL)).

[0038] The effective material percentage amounts to L_(NL) in theexample according to the invention, whereas M_(K) is formed as the sumof the individual values L_(NK1), L_(NK2), L_(NK3)

[0039] The inventive light metal cylinder block therefore comprises awear-resistant cylinder running face which is tribologically optimisedas a result of the uniform distribution of the fine Si primaryprecipitations and which, due to linear focussing and overlappingtreatments, can be produced at reduced production costs.

[0040] This is illustrated by the structure shown in FIG. 4 a high is amicro-section shown in a 200: 1 enlargement, with the righthand half Aof FIG. 4 showing a cast alloy of type AlSi₉ Cu₃ and the lefthand half Bof the Figure showing a tribologically optimised surface layer withfinely dispersed primary silicon precipitations. In the present example,the primary Si percentage amounts of 10%, the primary phase diameter to4.4 μm and the distance between the Si primary phases to 13 μm.

[0041] As far as the load bearing capacity of the new material isconcerned, particular significance has to be attached to the bonding ofthe alloyed-on zone B with the matrix structure A. It can be seen at themicro-section 4 that the transition zone C does not contain any oxidesor other defects. This is due to the fact that the alloyed-on zone wasproduced practically “in situ” from the matrix structure, thus achievinga uniform material with different compositions in regions A and B.

[0042] List of Reference Numbers Appearing in the Figures

[0043] 1. powder supply means

[0044] 1a end of powder supply means

[0045] 1b nozzle

[0046] 2. laser beam device

[0047] 3. focussing system

[0048] 4. deflecting mirror

[0049] 5 running face

[0050] 6 laser beam

[0051] 7 running face surface

[0052] 8 Cylinder axis

[0053] 9-

[0054] 10. alloyed-on zone

[0055] 11. zone high in precipitations

[0056] 12. 13 zone low in precipitations

[0057] 14.-

[0058] 15,16,17 boundary zones

[0059] M_(K) percentage of material

[0060] L_(NK) effective length of structure high in precipitations

[0061] L_(NL) effective length of zone high in precipitations

[0062] L_(AL) percentage of zone low in precipitations

[0063] L_(AK) regions associated with the interface zones

[0064] DH_(WK) material removed in comparative example

[0065] DH_(WL) material removed in example according to the invention

[0066] A matrix structure

[0067] B alloyed-on zone

[0068] C transition zone

What is claimed:
 1. A light metal cylinder block having at least onewear-resistant and tribologically optimized cylinder running facecompromising a light metal matrix alloy with a finely, dispersed surfacelayer containing primary silicon phases wherein the primary siliconcomprises uniformly distributed approximately roundly formed grains witha medium grain diameter ranging between about 1 and about 10 μm andWherein the surface layer contains about 10 to about 14% AlSi eutectic,about 5 to about 20% primary silicon, the remainder being pure Al phase,and wherein the minimum hardness of the surface amounts to about 160 HV.2. The light metal cylinder block according to claim 1, characterized inthat the silicon-primary phases are distributed in the surface layer ata distance of about 1 to about 5 times a primary phase diameter.
 3. Thelight metal cylinder block according to any claim 1, characterized inthat the primary silicon is arranged in a strip-like alloyed-on zonecomprising one or more strips with a strip width of at least about 2 mmand a medium layer thickness of about 50 to about 650 μm in the matrixalloy, with the strips extending spiral-like across the cylinder runningface.
 4. The light metal cylinder block according to claim 3,characterized in that the strip width amounts to about 2 to about 4 mm.5. The light metal cylinder block according to claim 3, characterized inthat if there are adjoining alloyed-on zones, the strips overlap, withthe width of overlap amounting to about 5 to about 10% of the stripwidth.
 6. A light metal cylinder block having at least onewear-resistant and tribologically optimized cylinder running face,comprising a light metal matrix alloy with a finely dispersed surfacelayer which contains primary silicon precipitations and which, as a purediffusion layer comprises an alloyed-on zone high in precipitations andof interface zones low in segregations, wherein the segregationscomprise uniformly distributed. approximately roundly formed primarySilicon grains with a mean grain diameter- ranging between about 1 andabout 10 μm and herein the alloyed-on zone comprises about 10 to about14% AlSi cutectic about 5 to about 20% primary silicon. the remainderbeing pure aluminum phase. and comprises a minimum hardness of about 160HV
 7. A method of producing a light metal cylinder block having at leastone wear-resistant and tribologically optimized cylinder running facecomprising a light metal matrix alloy and a powder material whichcontains a hard material and which is present in the form of a finelydispersed surface layer with primary silicon precipitations in the lightmetal matrix, using a gravity low-pressure or high-pressure die castingmethod with subsequent surface treatment by parallel laser and powderbeams wherein the laser beam is guided in a strip width of at leastabout 2 mm transversely to the direction of feed across the matrixsurface and wherein it is only in the point of impact of the laser beamon the light metal matrix surface in a contact time of about 0.1 toabout 0.5 seconds, that the powder is heated to melting temperature anddiffused in.
 8. The method according to claim 7, characterized in thatthe light metal matrix alloy, at the point of impact, at a depth of atleast about 350 μm, is fully melted and transferred on the light metalmatrix surface into the plasma condition.
 9. The method according toclaim 7, characterized in that, during diffusion, the melted powderforms an alloyed-on zone which comprises a layer thickness of about 500to about 1000 μm.
 10. A method according to claim 7, characterized inthat, at the point in time shortly before hitting the metal matrixalloy, the powder comprises a grain structure and that it is onlythrough contact Kith the metal matrix alloy in the region of the laserbeam that the powder is melted and alloyed-in within a contact time ofabout 0.1 to about 0 5 seconds.
 11. A method according to claim 7,characterized in that the feed speeds of the laser beam and of thepowder beam are controlled in such a way that: a) diffusion into themetal matrix alloy takes place achieving penetration depths about 350 toabout 850 μm; b) as a result of controlled slow cooling of thealloyed-on zone there are produced approximately roundly formed primaryphases smaller than about 10 μm, with the distance between sameamounting to about 1 to about 5 times the primary phase diameter; and c)precipitation of hard phases with a layer hardness of about 110 to about160 HV is achieved.
 12. The method according to claim 11, characterizedin that the speed of feed of the powdered metal beam amounts to about0.8 to about 4.0 m per minute with a focused impact area of the laserbeam of about 1 to about 10 mm² and a laser light output of about 3 toabout 4 kW.
 13. A method according to claim 7, characterized in thelaser beam rotates spirally with a linear focus on the inner runningface of the hollow cylinder and, in the process, with Si powder beingadded, forms a strip-like alloyed-on zone containing primary silicon.14. A method according to claim 7, characterized in that the meantreatment depth of the alloyed-on zone amounts to about 750 μm.
 15. Amethod according to claim 7, characterized in that the hard phases ofthe alloyed-on zone are exposed by machining, with the removal of theuppermost layer amounting to less than about 30% of the total layerthickness.
 16. A method according to claim 7, characterised in that thealloyed-on zone is honed directly, without an intermediate machiningoperation being carried out.
 17. A device for coating the a runningsurface of a hollow cylinder comprising powder supply means (1) a laserbeam device (2) and a focusing system (3) with a deflecting mirror (4),characterized in that the powder supply means (1) and the laser beamdevice (2) are guided parallel relative to one another in the radial andaxial direction of the hollow cylinder. that the focusing system (3)comprises a linear beam exit with a beam width of about 2.0 to about 2.5mm; and that the powder supply means are provided with a metering deviceby means of which the volume flow of the powder can be set as a functionof the speed of feed of the laser beam.
 18. The device according toclaim 17, characterized in that the focusing system (3) comprises an X-,I- or 8-like focus shape which, in the upper and lower surface zones.permits a higher energy output than in the central focus region.